Sequence-based Lithofacies And Paleogeography Of Feixianguan Formation, Lower Triassic In Eastern Sichuan And Northern Chongqing Area

The Feixianguan Formation of Lower Triassic in Eastern Sichuan and Northern Zhongqing area is mainly research objects of the thesis.Guided by the theories of sedimentology , carbonate reservoir geology and sequence stratigraphic,by sequence stratigraphic search,and on the basis of analysis of the rock structure , surface profile and drilling datas ,sequence-based lithofacies and paleogeography of the Feixianguan Formation ,Lower Triassic in Eastern Sichuan and Northern Zhongqing area has studied in detail, obtains the following several research results and the progress:1)The carbonate rocks' deposition combination and evolution characteristic of the Feixianguan Formation of Lower Triassic in Eastern Sichuan and Northern Zhongqing area conforms to Reed's carbonate platform concept and the depositional mode.The carbonate platform (facies) could be classified into 5 subenvironments: restricted platform, open-platform, bars in platform margin , slop and platform-basin,and further classified into 12 micro-environments including in the Oolitic bank in platformand the Oolitic bank in platform margin. The sedimentary models for the carbonate platform of the Feixianguan Formation of Lower Triassic in Eastern Sichuan and Northern have been established2)The Feixianguan Formation of Lower Triassic in the northeast Sichuan can be divided into 2 third-order sequences, six system tracts in terms of sedimentary facies and sequence interfaces. Characteristics of sequence stratigraphy of the Feixianguan Formation are analyzed, sequence-palaeogeography maps compiled. It is indicated that, during the development of SQ1 sequence ,influenced of the regional tectonic uplifting of the Changxing Stage of Late Permian in the study area,the product formed in a regional slow transgression-regression depositional environment.The seawater once deep and wide opening became shallow, the depositional evolution changed from basin facies to open-platform facies which almost formed the platform edge or inner oolitic bank. In the second deposition of the third-order sequence cycles(SQ2), due to arider and hotter climate,sea level falling and water cycle limiting,the sedimentary facies became to restricted platform and evaporate platform facies, and the oolitic bank disappeared gradually.Finally, the sedimentary facies tuned to evaporate platform in which gypsodolomite was developed. The gypsodolomite is the important sealant in the Feixianguan formation. and the brine saved in the same time is helpful to the burial dolomitisation in the oolitic bank to form high quality reservoir in the Feixianguan formation.3)The Oolitic bank in platform(facies) is the sedimentary facies superiority constitutes in the pattern of the local various Sequence-based– lithofacies and palaeogeography in Eastern Sichuan and Northern Zhongqing area. The well drilling main force produces layer in the advantageous reservoir growth in Eastern Sichuan and Northern Zhongqing area is bringed by the Oolitic bank in platform(facies) including in the Oolitic bank in platform and the Oolitic bank in platform margin.The Oolitic bank in platform(facies) in TST of SQ1, TST of SQ2,and EHST of SQ2 (the third-order sequence) in Eastern Sichuan and Northern Zhongqing area,specially the Oolitic bank deep buried dolomitization , should become present's exploration key.